The present invention relates to a camera having a red-eye forecasting device, and in particular to a camera having a device for forecasting and alarming a photographer of red-eye phenomenon which occurs when taking a picture of a person or persons by using an electronic flash.
It has been well-known for a long time the red-eye phenomenon that people with glowing red eyes are photographed depending upon the distance between an optical axis of a taking lens of a camera and the center of an electronic flash when using the flash.
Various techniques to prevent such red-eye phenomenon have been disclosed in Japanese Laid-open Utility Model Application Sho No. 54-53429, Japanese Laid-open Patent Application Sho/No. 62-2238 and Japanese Patent Publications Sho/No. 58-20021 and Sho/No. 58-48088.
Japanese Laid Open Utility Model Application Sho No. 54-53429 discloses a camera which is adapted to satisfy a given angle .alpha.=tan.sup.-1 (d/l) in which a red-eye phenomenon is prevented by changing the distance d between an optical axis of a taking lens and the center of an electronic flash depending upon the distance l between an object to be photographed and the camera as shown in FIG. 8.
Japanese Patent Publication Sho No. 58-48088 discloses a camera in which a regular electronic flash photographing operation is conducted so that glowing red-eyes are not prominent after conducting preliminary flashing to reduce a pupil diameter at a dark place. This is based on the fact that the red-eye phenomenon occurs when photographing is conducted by using a flash in a dark place while a person has widely open pupils.
Japanese Laid-open Patent Application Sho No. 62-2238 discloses a camera having two short and long focal length taking lenses in which an electronic flash is adapted to be moved away from the taking lens when photographing is conducted by using the long focal length lens in which a magnified red-eye readily occurs.
Japanese Patent Publication Sho No. 58-2002 suggests that factors of red-eye phenomenon include four factors as follows:
(1) brightness level at the photographing site (Bv);
(2) light emission amount (GNo) of a built-in electronic flash;
(3) the distance d between the optical axis of a taking lens of a camera and the center of a light emitting tube of a built-in electronic flash; and
(4) the distance (l ) between the eyes of a person to be photographed and a camera. Japanese Patent Publication Sho/No. 58-20021 also mentions a formula showing the relation between GNo and d which is a condition of red-eye phenomenon.
Although Japanese Laid Open Utility Model Application Sho No. 54-53429 discloses a camera in which a light emission portion is moved in relation to an object distance l, it does not mention the condition of redeye phenomenon. It is troublesome for photographers to move a light emission portion even in a light environment where red-eye phenomenon does not occur.
This is the same as Japanese Laid-open Patent Application Sho No. 62-2238. There is no description of the condition of red-eye phenomenon. It is irrational and inconvenient to move an electronic flash every time when photographing is conducted.
Japanese Patent Publication Sho No. 58-48088 has never determined the condition of red-eye phenomenon and aims at preventing the red-eye phenomenon by photographing with a pupil contracted due to preliminary light emission. A photographer has to wait about 1.6 seconds from the preliminary light emission to the contraction of a pupil. Therefore a shutter chance may be lost. The photographer does not know when preliminary light emission should be conducted since the condition of red-eye phenomenon is not determined.
The Japanese Patent Publication Sho No. 58-20021 mentions the relation between the GNo and a distance d between a taking lens and an electronic flash and suggests a range of the relation where red-eye phenomenon occurs. But it is not too much to say that GNo is not related with red-eye phenomenon since red-eye phenomenon takes place on a film. Red glowing eyes having a suitable brightness are photographed on a film independently of GNo as far as photographing is conducted on proper exposure. This prior art determines GNo and a distance d assuming the focal length of a taking lens be about 38 mm. It is not meaningful to determine the conditions of red-eye phenomenon based upon only these GNo and d since compact cameras having two focal points and compact cameras having a zoom lens are presently in widespread use, resulting in a significant increase in the frequency of high magnification photographing.